Conventional known paper containers with a window are, for example, those described in Patent Document 1, Patent Document 2, and Patent Document 3. Patent Documents 1 to 3 each describe a paper container with a paper layer provided with a cutout part that is covered with a transparent material. In Patent Document 1, however, there is no description about a gas barrier material. On the other hand, Patent Documents 2 and 3 each describe that a cutout part is covered with a gas barrier material. The gas barrier material described in Patent Document 2 is a metal oxide-deposited, biaxially-oriented plastic film, and examples of the gas barrier material described in Patent Document 3 include films of, for example, polyvinyl alcohol and a saponified ethylene-vinyl acetate copolymer, films formed by coating, for example, polyethylene terephthalate, polyamide, polyvinyl alcohol, or a saponified ethylene-vinyl acetate copolymer with polyvinylidene chloride, and films subjected to vapor deposition of an inorganic material, such as silicon oxide or aluminum oxide.
Recently, however, with an increase in applications of paper containers where increasingly higher barrier properties are required, sufficiently high gas barrier properties for such applications cannot be obtained by films of, for example, polyvinyl alcohol and a saponified ethylene-vinyl acetate copolymer, or films formed by coating, for example, polyethylene terephthalate, polyamide, polyvinyl alcohol, or a saponified ethylene-vinyl acetate copolymer with polyvinylidene chloride. In the films obtained by vapor depositing an inorganic material such as silicon oxide or aluminum oxide on, for example, polyethylene terephthalate, polyamide, polyvinyl alcohol, or a saponified ethylene-vinyl acetate copolymer, since the inorganic material layer lacks in flexibility, defects tend to be caused when they are subjected to bending or impact and the gas barrier properties may be deteriorated during the production or transportation of the containers. Accordingly, they are not satisfactory in terms of productivity, and they also lack in reliability as containers.
A laminate in which paper is used as a substrate and one surface to be located on the inner side of the container or both surfaces thereof are laminated with low density polyethylene having, for example, heat adhesiveness and water resistance is used for a paper container. When a paper container is to be subjected to a retort sterilization process, heat-resistant polyolefin such as linear low density polyethylene resin, high density polyethylene resin, or polypropylene resin that has high heat resistance and heat adhesiveness is selected instead of the low density polyethylene.
Furthermore, a laminated material is described in Patent Document 4, in which aluminum, aluminum oxide coating, silica coating, metalized oriented polyester, metalized oriented polypropylene, metalized (usually with aluminum) oriented polyester, metalized (usually with aluminum) oriented polypropylene, ethylene/vinyl alcohol, or polyvinyl alcohol is included as a barrier layer when a paper container is required to have gas barrier properties.
However, when aluminum, aluminum oxide coating, silica coating, metalized oriented polyester, or metalized oriented polypropylene is used for a gas barrier layer, there is a problem in that since the gas barrier layer does not have sufficiently high durability against bending during formation thereof, the gas barrier layer has poor formability and pinholes tend to be formed during the formation of paper containers to impair the barrier properties thereof considerably. Furthermore, in the case of using aluminum, there is a problem in that when the paper container is disposed by, for example, incineration, aluminum remains and therefore it is not suitable in terms of disposal. Furthermore, there also is a disadvantage in that the contents cannot be warmed with a microwave oven in the case of a product including food packaged in a paper container in which metal such as aluminum is used.
On the other hand, when, for example, ethylene/vinyl alcohol, ethylene/vinyl alcohol containing polyvinyl alcohol, or polyvinyl alcohol is used, it has a certain degree of durability against bending but the gas barrier properties thereof degrade in the wet condition. Accordingly, when it is subjected to a process in a high-temperature water-wet condition, such as a retort process, the gas barrier properties tend not to be exhibited satisfactorily.
As described above, currently there are no paper containers that can be subjected to a retort process, that have a high forming processability, and that have sufficiently high gas barrier properties in various shapes.
Conventionally, heat insulators containing polyurethane foam have been used as heat insulation materials for refrigerators and insulation panels for insulated walls for housing. Recently, however, a vacuum heat insulator composed of a gas barrier laminate film and a core material is used as a better material that replaces the above-mentioned heat insulators. Mainly, aluminum foil is used as a gas barrier material but aluminum is a good conductor of heat. Therefore the phenomenon that heat transfers through the aluminum portion of a laminate film, i.e. so-called “heat bridge” occurs and thereby the heat insulation performance is deteriorated.
In order to solve the problem of heat bridge, there are attempts to reduce the thickness of the metal layer and to use a gas barrier material having a gas barrier layer formed using metal oxide instead of metal. In other words, there is a method in which a gas barrier material including a deposited layer as a gas barrier layer is used, wherein the deposited layer is formed by vapor depositing metal such as aluminum or metal oxide such as silica or alumina on the surface of a film such as a polyester film or an ethylene-vinyl alcohol copolymer film. For example, Patent Document 5 describes a vacuum heat insulator including a gas barrier layer formed by vapor depositing aluminum on a film made of ethylene-vinyl alcohol copolymer resin.
However, pinholes tend to be formed in deposited layers obtained by the vapor deposition method, and defects such as pinholes tend to occur in deposited layers in producing laminate films or transporting the products. As a result, the gas barrier properties are poor and are not exhibited stably, and thereby there is a problem in reliability.
In order to solve such a problem, Patent Document 6 proposes a vacuum heat insulator including a gas barrier material having a gas barrier layer composed of resin and an inorganic layered compound that is used on top of a deposited layer formed of a compound of metal such as alumina that has been deposited on a substrate resin. However, the gas barrier properties thereof are still not sufficiently high and the heat insulating effect cannot be maintained satisfactorily over a long period of time.
Conventionally, glass containers that are excellent in transparency, storage stability, and heat resistance are used as infusion containers. However, glass containers have problems in that, for instance, they tend to be damaged by impact, are heavy, tend to generate glass flakes, and generate insoluble fine particles. Plastic containers have come to be used widely as infusion containers, since they solve these problems. There are plastic infusion containers in the form of a bag and those in the form of a bottle.
Infusion bags in the form of a bag are made of, for example, polyolefin resin such as polyethylene or polyvinyl chloride resin. The polyolefin resin cannot be considered to have sufficiently high gas barrier properties and has a problem in that infusion solutions such as amino acid preparations, glucose preparations, fat emulsion preparations, or electrolyte solutions, with which the infusion bags are filled, tend to be deteriorated by gas such as oxygen. Since the polyvinyl chloride resin contains additives such as a plasticizer and a stabilizer, there is a fear of elution thereof. As described above, there is a problem in that the polyolefin resin has poor gas barrier properties.
Accordingly, when a drug solution such as the above-mentioned amino acid is enclosed, the outer side of an infusion bag made of, for example, polyolefin was double-packaged with a bag having gas barrier properties that have been prepared separately, i.e. with an outer packaging material such as a multilayer film formed using ethylene-vinyl alcohol copolymer resin and polyvinylidene chloride as constituent materials, for instance, a multilayer film formed of a polyester layer/ethylene-vinyl alcohol copolymer layer/non-oriented polypropylene layer (see, for instance, Patent Document 7). However, in the method in which a separate outer packaging material is used, once the outer packaging material is opened, for example, for mixing a drug solution thereinto, air tightness is lost. Accordingly, the content thereof needs to be used within a short period of time thereafter. For such usage, it is desired that gas barrier properties be imparted to infusion bags themselves.
Methods of imparting the gas barrier properties to infusion bags themselves also are proposed in, for example, Patent Document 8 and Patent Document 9. Patent Document 8 describes an infusion bag formed using a polyamide resin. However, such polyamide resin does not have sufficiently high barrier properties for applications that require a high degree of gas barrier properties and tends to have degraded barrier properties when being subjected to high temperature steam sterilization. Patent Document 9 descries an infusion bag whose outer surface is provided with a gas barrier coating material layer formed thereon, which is then coated with a protectant. However, the barrier layer described therein, for example, deposited alumina or silica, has poor flexibility. Accordingly, there are concerns that the bag is damaged during transportation or handling thereof and the barrier properties are degraded. Furthermore, when EVOH, PVA, or PVDC is subjected to high temperature steam sterilization, barrier properties thereof are degraded. Moreover, since PVDC contains chlorine, care needs to be taken during disposal and incineration thereof.
Recently, containers with a cover, each of which is composed of a cover member and a cup or tray having a flange portion, are used often as containers for preserving contents such as foodstuffs. In these containers with a cover, it is necessary to impart oxygen gas barrier properties not only to the containers such as cups or trays but also to cover members depending on the type of contents. Therefore it has been proposed conventionally to use, as a cover member, a laminate including another film laminated on a film with excellent oxygen gas barrier properties such as a film formed of polyvinylidene chloride resin (hereinafter described as a “PVDC film”), a film formed of an ethylene-vinyl alcohol copolymer (hereinafter described as a “EVOH film”), or a deposited film having a deposited layer of an inorganic material such as silica, alumina, or aluminum on a substrate film (hereinafter described as a “deposited film”). For example, Patent Documents 10, 11, and 12 describe a cover member including a PVDC film, a cover member including an EVOH film, and a cover member including a deposited film, respectively.
When a PVDC film is used for a cover member, the oxygen barrier properties thereof may meet desired performance although it also depends on the contents to be packaged in the container with a cover. However, when it is disposed as waste after being used as a cover member, there is a problem in that, for example, it causes poisonous gas such as dioxin to be generated upon incineration and therefore the environmental suitability is impaired.
Furthermore, when an EVOH film is used, it exhibits excellent oxygen barrier properties in a low humidity atmosphere. However, there is a problem in that when the EVOH film absorbs moisture, the oxygen barrier properties thereof are degraded.
Moreover, when a deposited film is used, there is a problem in reliability to gas barrier properties, that is, an inorganic deposited layer that serves as a gas barrier layer tends to crack and have degraded gas barrier properties. Gas barrier properties may be degraded due to, for example, cracks caused in a printing process or a lamination process through which a multilayer laminate is produced with a deposited film and another film, or cracks caused in a gas barrier layer due to vibrations during transportation when a number of containers with a cover are to be transported, with respective containers with a cover being stacked together.
Laminate tube containers that are used for packaging cosmetics, chemicals, pharmaceutical agents, toiletry articles such as toothpastes, and foodstuffs such as a mustard paste and a green horseradish paste are required to have excellent gas barrier properties and aroma retention properties. Accordingly, laminate materials formed using a resin film having aluminum foil or a deposited aluminum layer are often used conventionally. However, since the laminate material cannot be made transparent, the design of packaging materials is limited. Furthermore, since it is difficult to see the contents through it, it is not easy to check, for example, deterioration or remaining amount of the contents and further it was inconvenient for squeezing all the contents out thereof. Moreover, when the tube containers are used as packaging containers and thereafter are disposed as waste, since aluminum remains, they lack disposability and remaining aluminum damages incinerators, which are problems.
Examples of the gas barrier film having transparency and excellent disposability include a transparent deposited film having a deposited layer formed of inorganic oxide by a vacuum vapor deposition method, a film formed using polyvinylidene chloride resin, and a film formed using an ethylene-vinyl alcohol copolymer. These films also are used for laminate tube containers (see, for instance, Patent Documents 13 and 14).
However, the transparent deposited films tend to have defects such as cracks caused in a deposited layer that serves as a gas barrier layer in the processes for manufacturing a laminate tube container, for example, a printing process and a lamination process. Furthermore, when the laminate tube containers are squeezed, defects such as cracks also tend to be caused. As a result, the transparent deposited film has poor gas barrier properties.
The film formed using polyvinylidene chloride resin has a problem from an environmental viewpoint because when the laminate tube container is used as a packaging container and is then incinerated as waste, harmful gas such as dioxin may be generated.
The ethylene-vinyl alcohol copolymer is an excellent barrier film from all of the viewpoints of gas barrier properties, transparency, and environmental friendliness. However, the ethylene-vinyl alcohol copolymer has a problem in that when it absorbs moisture, the gas barrier properties thereof are degraded.
Conventionally, vacuum packaging characterized in that contents such as corn on the cob, tea leaves, coffee beans, meat, fish, and confectionery each are enclosed in a bag-type article and then the inside thereof is deaerated under reduced pressure has been employed widely as an effective method for preventing chemical changes and microbial changes of the contents to preserve them for a long period of time. Although heat sterilization is carried out after vacuum packaging in many cases, another method also may be employed in which contents are vacuum-packaged in a sterile state and are not subjected to heat sterilization. In both cases of carrying out and not carrying out heat sterilization, in order to prevent the microbial changes and chemical changes for a long period of time after vacuum packaging, the inside of the packaging material needs to have a low oxygen concentration, and therefore a material that has high gas barrier properties and can change its shape easily according to the contour of foodstuffs is used as a material for vacuum packaging.
Such materials for vacuum packaging having high gas barrier properties that have been used up to now include laminates, each of which has, as a gas barrier layer, a polyvinylidene chloride resin layer, a saponified ethylene-vinyl acetate copolymer (EVOH) layer, an aluminum foil layer, or a deposited layer formed of, for example, silicon oxide or aluminum oxide. However, all the laminates have the problems described below and are not satisfactory as materials for vacuum packaging. Recently, there is a tendency to refrain from using the laminates including an aluminum foil layer and those including a polyvinylidene chloride resin layer in consideration of the environment. The laminate containing aluminum foil and the laminate including a polyvinylidene chloride resin layer have the following problems, respectively. When the laminate containing aluminum foil is incinerated after use, the aluminum foil remains as a residue. When the laminate including a polyvinylidene chloride resin layer is incinerated after use, a harmful compound containing chlorine may be generated. Furthermore, the following problems also have been pointed out. That is, the laminate including an aluminum foil layer is not transparent and therefore does not allow the state of contents to be checked or does not allow a metal detector to be used for inspection of the contents.
A laminate including, as a gas barrier layer, a deposited layer formed by vapor depositing inorganic oxide such as aluminum oxide or silicon oxide on a substrate film is transparent and has excellent gas barrier properties. However, cracks and pinholes are generated in the deposited layer due to deformation of the packaging material that occurs during vacuum packaging and thereby the gas barrier properties thereof are degraded. In other words, defects such as cracks and pinholes are caused in the deposited layer due to deformation of the packaging material that occurs according to the contour of contents, or due to bending at the boundary between a heat sealed portion and a portion that comes into contact with the contents. Furthermore, it also has problems in that cracks and pinholes are caused in the deposited layer to degrade the gas barrier properties thereof due to expansion and contraction caused during heat sterilization processing as well as shock and bending caused during handling the packaged products. Accordingly, there are attempts to improve crack resistance and pinhole resistance by further providing a resin layer on a deposited layer. However, the improvement effect thereof is not satisfactory and the use thereof as a vacuum packaging bag is limited at present. A laminate including, as a gas barrier layer, a saponified ethylene-vinyl acetate copolymer (EVOH) layer is excellent in gas barrier properties but has a problem in that the gas barrier properties are degraded by the heat sterilization process following the vacuum packaging.
Vacuum packaging carried out as described above prolongs shelf life of the contents, foodstuffs. However, if the contents are foodstuffs containing solids, the packaging bag is deformed according to the contours of the foodstuffs and also is bent at the boundary between the heat sealed portion and a portion that is in contact with the foodstuffs, and thereby the gas barrier properties are degraded, which results in shorter shelf life of the foodstuffs. At present, there are still no packaging bags that have solved the problems concerning the environment and safety that have been highlighted recently and have solved the aforementioned problems accompanying the vacuum packaging.
Conventionally, liquid agents such as, for example, liquid detergents, shampoos, and conditioners, liquid beverages such as soft drinks, as well as liquid or fluid foodstuffs are packaged in rigid containers such as glass bottles, metal cans, or plastic bottles. However, such containers result in high packaging material cost and have poor disposability because the packaging materials cannot be reduced in volume at the time of disposal. Accordingly, plastic film pouches with a spout part formed in one sealing surface are used widely as lightweight, inexpensive, easy, and simple containers that are used for packaging recently. Pouch containers with a spout include those of a standing type (FIG. 1) and a pillow type (FIG. 2).
The plastic film and layer structure to be employed for a pouch with a spout can be selected according to the properties of contents to be packaged in the pouch. For example, a laminated film with a two-layer structure can be used for a pouch that is required to be produced at low cost, such as a packaging bag for a detergent refill. However, when contents that are required to have storage stability, such as beverages, seasonings, and pouch-packed food are to be packaged, it is preferable to use a laminated film with at least three layers including a barrier layer formed of a film provided with aluminum foil or an inorganic deposited layer, a gas barrier resin film, or a film obtained by coating any one of them.
With respect to a method of imparting gas barrier properties to pouches including a pouch with a spout, a packaging bag formed using a polyamide resin has been proposed (see, for example, Patent Document 8). However, the polyamide resin as described above does not have sufficiently high barrier properties for applications that require a high degree of gas barrier properties and tend to have degraded barrier properties when being subjected to a retort sterilization process. Furthermore, there is a problem in that for example, vinylidene chloride or polyacrylonitrile may become a source of harmful substance at the time of disposal and incineration. Although metal foils are excellent in gas barrier properties, they have problems in that they do not allow contents to be seen through the packaging material to be checked, they do not allow a metal detector to be used for inspection, and they are environmentally undesirable because it is difficult to separate a metal layer from other layers for disposal after use and therefore they have to be treated as an incombustible. Moreover, the use of a plastic film having an inorganic oxide deposited layer such as an aluminum oxide deposited layer or a silicon oxide deposited layer was proposed. An inorganic oxide deposited layer is a thin film with a thickness of up to 800 Å, has transparency, and does not cause any environmental problems because it is treated in the same manner as in the case of printing ink and therefore is not required to be separated for incineration.
However, when these films are bent or impacted accidentally during packaging the contents or distribution, the spout-attached part or heat sealed portion of the spout pouch body, especially an edge portion thereof, may be damaged and the inorganic oxide deposited layer may be cracked, which causes degradations in gas barrier properties and steam barrier properties. In order to prevent the cracks from occurring, various studies are being made about resin coating or film laminate to serve as a protective layer on one surface or both surfaces of the inorganic oxide deposited film. Furthermore, similarly in the case where, for instance, retort cooking sterilization carried out after packaging of the contents causes the inner pressure to increase, the inorganic oxide deposited layer also may be cracked in the vicinity of the portion sealed to form a bag. However, due to its flexibility, a packaging bag formed of a film laminate cannot be prevented from being bent during packaging of the contents or distribution, or cannot prevent tension from occurring due to change in inner pressure during sterilization cooking. Thus there are disadvantages that damage occurs at the spout-attached part or heat sealed portion of the spout pouch body, especially an edge portion thereof, which results in degradation in gas barrier properties of the container.    Patent Document 1 JP 10 (1998)-194273 A    Patent Document 2 JP 2003-054537 A    Patent Document 3 JP 11 (1999)-227752 A    Patent Document 4 JP 11 (1999)-508502 A    Patent Document 5 JP 10 (1998)-122477 A    Patent Document 6 JP 11 (1999)-257574 A    Patent Document 7 JP 09 (1997)-262943 A    Patent Document 8 JP 2001-328681 A    Patent Document 9 JP 2005-040489 A    Patent Document 10 JP 57 (1982)-030745 B    Patent Document 11 JP 09 (1997)-239911 A    Patent Document 12 JP 2005-8160 A    Patent Document 13 JP 11 (1999)-129380A    Patent Document 14 JP 07 (1995)-308994A